Yes, actually looking at the plots, it is obvious that with some arbitrary phase drifts, you can get pretty good corelation. The shapes still look very similar, that is something. This could be resolved ofcourse only if someone can explain the drifts in the data without using orbital data. But I think it looks interestiing.

Can you give a reference or explain the 2-3 kyrs accuracy. Perhaps in the first 50 kyrs it might be that accurate, but not at say 500 kyrs.

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By: The Icebox Heats Up * The New World https://scienceofdoom.com/2014/02/02/ghosts-of-climates-past-fifteen-roe-vs-huybers/#comment-92930
Sun, 25 Jan 2015 08:48:20 +0000http://scienceofdoom.com/?p=8406#comment-92930[…] I’ll use the same temperature proxy dataset used in the discussion by Science of Doom here and here, which is the Huybers ∂18O dataset . For the insolation, I’m using the same Berger […]
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By: The Icebox Heats Up | Watts Up With That? https://scienceofdoom.com/2014/02/02/ghosts-of-climates-past-fifteen-roe-vs-huybers/#comment-92914
Sun, 25 Jan 2015 05:15:33 +0000http://scienceofdoom.com/?p=8406#comment-92914[…] I’ll use the same temperature proxy dataset used in the discussion by Science of Doom here and here, which is the Huybers ∂18O dataset . For the insolation, I’m using the same Berger […]
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By: Gary https://scienceofdoom.com/2014/02/02/ghosts-of-climates-past-fifteen-roe-vs-huybers/#comment-92700
Fri, 23 Jan 2015 20:29:56 +0000http://scienceofdoom.com/?p=8406#comment-92700I just discovered this post; however, it may be worth a note about the SPECMAP tuning work done 35 years ago . It’s true the O18 curves were tuned to orbital parameters but the tuning was constrained by half a dozen or so C14 and/or microfossil extinction dates in the deep sea sediment cores used. Bioturbation, sediment rates, and sampling intervals are going to make exact dates a bit fuzzy of course, but IIRC the dating accuracy was estimated to be within 2-3kyrs.
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By: Ghosts of Climates Past – Nineteen – Ice Sheet Models I | The Science of Doom https://scienceofdoom.com/2014/02/02/ghosts-of-climates-past-fifteen-roe-vs-huybers/#comment-63468
Mon, 02 Jun 2014 19:44:33 +0000http://scienceofdoom.com/?p=8406#comment-63468[…] Fifteen – Roe vs Huybers – reviewing In Defence of Milankovitch, by Gerard Roe […]
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By: Howard https://scienceofdoom.com/2014/02/02/ghosts-of-climates-past-fifteen-roe-vs-huybers/#comment-49145
Thu, 13 Feb 2014 15:09:37 +0000http://scienceofdoom.com/?p=8406#comment-49145In reply to Howard.

DeWitt and SOD, thanks for setting me straight on the gas problem in Antarctica. Looking forward to future posts. In no hurry, there is plenty to chew on as it is.

The gas age question is complicated and I expect to write more about it in a later article.

Fresh snow allows air to circulate. Eventually the snow compacts into ice and finally the structure locks the air in.

As DeWitt says, in Antarctica snow accumulation is very low which means the depth of air circulation before “close off” corresponds to many thousands of years. By contrast, in Greenland, the snow accumulation is much higher which means the same depth corresponds to a shorter time – and less age uncertainty.

There are a few approaches to determining gas age.

1. The ‘firn model’, which is based on how the crystalline structure changes with depth – this allows us to calculate the difference between age of ice and age of gas, so if the ice can be dated we can estimate the age of the gas.

Ice can be dated in a number of ways, not just from accumulation estimates (constraints from 10Be events, volcanic events..).

2. Synchronization of Greenland and Antarctica using CH4. We have better dating for Greenland ice for at least 50,000 years by counting layers (higher accumulation rates in Greenland makes this possible). And the gas-ice age difference is lower in Greenland as mentioned above.
CH4 is a well-mixed gas globally, is captured in both Greenland and Antarctica ice cores and has significant variability over the thousand year timescale – so we can match up Greenland and Antarctica gas age – at least during periods of significant CH4 change.

Unfortunately, the best Greenland ice core (NGRIP) only goes back 123,000 years because it all melted prior to this date.

3. δ18O(atm) – in many of the graphs produced in this series we have seen δ18O from the ice as a proxy for temperature when it snowed out – also we can measure δD from ice which works on the exact same basis.

We also have measurements of δ18O in the gas trapped in the ice – this is the isotope of oxygen in the air, rather than in the ice. It appears that there is a strong correlation of δ18O(atm) with insolation changes and this presents the opportunity to at least count precession cycles (ie we can ensure that older dates have accuracies constrained to at least +/- 10,000 years – half a precession cycle).

4. Novel methods, which I am just reading up on at the moment. These include N2/O2 ratios, volume of air trapped in the ice, fractionation of isotopes (like 15N) due to thermal and gravitational effects.

If anyone is interested in papers which explain any of these points, just ask.

Otherwise these points will all get covered in future articles along with references, and I will do a better job than the brief note above of explaining how all this fits together.

Yes and no. The dust/temp relationship with time is solid. CO2 has problems because the bubbles may not seal for a very long time. During the depths of a glacial period, snow accumulation in central Antarctica is very slow. The gas age and the ice age may differ by thousands of years, with the gas age always younger than the surrounding ice. Once all the 14C decays in ~50,000 years, the gas age can only be estimated from the estimated rate of accumulation.